The present invention relates to a pipe coupling, and in particular to a valve provided in a pipe coupling.
In a conventional pipe coupling comprising male and female couplers for interconnection with one another, generally the male coupler and/or the female coupler is provided with a valve for closing and opening a fluid passage existing within the pipe coupling. The valve generally has a valve head provided with a sealing ring adapted to be engaged with and disengaged from a valve seat upon axial movement of the valve within the fluid passage. (Shown in JP Utility Model Publication No. S58-187687)
FIG. 5 shows part of a valve head 54 of a conventional-type valve 50 provided in a coupler fluid passage 52 formed, in this example, in a male coupler 51. The valve 50 comprises a valve head 54 having a tapered annular surface corresponding to a valve seat 53 formed in an interior surface of the coupler 51 defining the fluid passage 52. The tapered annular surface of the valve head is formed to have an annular groove 55 in which a sealing ring 56 made of rubber is disposed. The valve 50 is axially movably mounted in the fluid passage 52 and urged forward by a spring (not shown) so that the sealing ring 56 is sealingly engaged with the valve seat and, upon imposition of a rearward force on the valve 50, the valve is moved rearward and disengaged from the valve seat 53. As shown in the figure, a right side wall 57 of the annular groove 55 is inclined so as to hold the sealing ring between the right side wall 57 and a left side wall of the same, to thereby prevent the sealing ring from moving out from the annular groove 55.
When the valve 50 is operated to close the fluid passage 52, and the closed fluid passage is filled with a high pressure fluid, there is a possibility that the high pressure fluid will permeate into the interface between the sealing ring 56 and the side wall of the annular groove, and down to the bottom 59 of the annular groove 55. In such a case, if the fluid passage, into which a high pressure fluid has been filled, is subject to a sudden decrease in pressure resulting from, for example, discharge of the high pressure fluid, a large pressure difference will be generated between the outside or the fluid passage and bottom side of the annular groove. If this occurs, the sealing ring is liable to be dislodged from the annular groove 55 under the action of the high pressure fluid which has permeated down to the bottom of the annular groove.